1. Field of the Invention
The present invention relates to a device for humidifying the useful space of a climatic chamber. More particularly, the humidifying device of the present invention having a completely closed water-holding reservoir defined by watertight walls, at least part of the reservoir being made of material that is permeable to water vapor, but is impervious to liquid water.
2. Background Information
Climatic cabinets such as incubators or aerators/incubators of the various models described, for example, in brochures of Heraeus Instruments GmbH are usually equipped with an open trough containing a water supply for continuously humidifying the atmosphere of the useful volume to a relative humidity of about 95%. At temperatures such as 37.degree. C., environmental conditions as close as possible to natural conditions are simulated for the cell and tissue cultures growing "in vitro" in such incubators. Contamination by fungi, bacteria or Mycoplasma species must be absolutely prevented, since it can destroy valuable cultures or lead to false study results. Open humidifying devices therefore always represent a potential source of contamination, which can be kept under control only by elaborate cleaning procedures. Moreover, water spills that must then be dried up again can easily occur when the water reservoir is being removed or filled. The walls of the useful space of a climatic cabinet themselves must be kept as dry as possible, in order to exclude the possibility of accumulations of dirt and contamination.
A certain useful volume corresponding to its dimensions is reserved for the usual humidifying device with an open water reservoir. Such water reservoirs cannot be placed conveniently in positions other than provided by design. In the individual case, this may mean that the cell cultures are not optimally humidified. Additional water reservoirs can certainly be placed in the climatic cabinet or incubator, but they then reduce the usable volume available to the culture vessels. Furthermore, the free water surface is naturally limited by the construction of the reservoir. On the other hand, a large surface area for evaporation of the water is desirable in order to increase the efficiency of the humidifying device.
A trough-shaped reservoir with an opening spanned by a water-vapor-permeable membrane is also known from DE 36 41 821 A 1. In this case the reservoir functions as a moisture source for a measuring technique for testing the water-vapor permeability of materials. The measurements are performed in a climatic cabinet. As in the cited prior art, this humidifying device also suffers from the disadvantages of a trough that allows little variation in use thereof, occupies a relatively large space, provides only a small surface area for releasing water vapor and has elaborate means for closing and fixing the membrane.
U.S. Pat. No. 4,622,049 discloses a two-compartment test device with a supply reservoir of saturated aqueous saline solution in the lower compartment. In this case also the humidifying device consists of a fixed trough, wherein a small part of that surface of the said trough which faces the second, upper compartment is provided with a water-vapor-permeable membrane or with glass wool. The dimensions of the upper and lower compartments are matched such that they can be coupled form-fittingly together, and so the device can be regarded as a total system. Thus this device also merely represents a further variant of the already described general prior art (fixed water reservoir/trough).
From WO 94/29650 there is also known an air-humidifying system for climatic installations, which system contains one section with water-vapor-permeable membranes. The membranes are clamped in a fixed frame, and the water is passed between two membranes designed as filters for microbes, particles and dissolved salts. The water-supply reservoir is connected separately and via a piping system with the membrane frame. The section constructed as the membrane cell is bounded by membranes on two sides. The frame and the membrane-clamping means impart a rigid form to the overall construction, and so here also a fixed reservoir with the known disadvantages is obtained.
A so-called scent bag is known from U.S. Pat. No. 4,961,493. In this case a substance containing a liquid or gel-like fragrance or perfume is held in a gas-permeable, but liquid-tight bag. The bag cannot be refilled without destroying it, and its purpose is to freshen the air, at a temperature of about 25.degree. C., in living rooms or passenger vehicles, where strict requirements of sterility or autoclavability are not a concern. The container is designed as a disposable article, which loses its function as a source of gaseous fragrances after some time and, since it cannot be refilled, must be replaced by a new fragrance bag. This bag is completely unsuitable for use in well defined atmospheres such as are necessary in climatic cabinets.